Method and apparatus for controlling metal strip shape

ABSTRACT

A process and apparatus for rolling a metal strip whereby the waviness of the strip in the direction of the strip thickness is detected at a plurality of locations along the width of the strip, while the strip is under tension, during the rolling operation. The roll crown and/or the rolling load is selectively controlled in response to the detected waviness Delta h in accordance with the relation Delta h Embij + F, where i and j are variables indicating the position of sensors, m is a parameter relating to tension of the strip, b is the output waviness under no tension and E and F are constants. The shape variations b in the resulting output metal strip, under no tension, which are not actually determined until after a very long period of time, such as during the next manufacturing process, are maintained within predetermined tolerances by said preliminary control during the rolling operation.

United States Patent [191 Kubo et al.

[ Sept. 4, 1973 METHOD AND APPARATUS FOR CONTROLLING METAL STRIP SHAPE[75] Inventors: Moritada Kubo, Tokyo; Kuniji Asano; Takashi Kusakabe,both of Kawasaki, all of Japan [73] Assignees: Nippon Kokan KobushikiKaisha,

Tokyo; Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan 22 Filed:Mar. 6, 1972 [21] App]. N0.: 232,115

Related US. Application Data [63] Continuation-in-part of Ser. No.838,282, July 1,

l969, abandoned.

[30] Foreign Application Priority Data July 3, 1968 Japan 43/46l08 [52]US. Cl. 72/9, 72/12 [51] Int. Cl B2lb 37/12 [58] Field of Search72/8-12, 72/16 [56] References Cited UNITED STATES PATENTS 3,475,935ll/l969 Kajiwara 72/9 DETECTORS M.

RECTIFIERS CONVERTER CIRCUITS 3,496,744 2/1970 Mizuno et al 72/12Primary Examiner-Milton S. Mehr Attorney-Robert D. Flynn, Leonard l:lqlt z 1 a l.

[5 7 ABSTRACT A process and apparatus for rolling a metal strip wherebythe waviness of the strip in the direction of the strip thickness isdetected at a plurality of locations along the width of the strip, whilethe strip is under tension, during the rolling operation. The roll crownand- /or the rolling load is selectively controlled in response to thedetected waviness Ah in accordance with the relation Ah E b F where iand j are variables indicating the position of sensors, m is a parameterrelating to tension of the strip, b is the output waviness under notension and E and F are constants. The shape varia tions b in theresulting output metal strip, under no tension, which are not actuallydetermined until after a very long period of time, such as during thenext manufacturing process, are maintained within predeterminedtolerances by said preliminary control during the rolling operation.

13 Claims, 11 Drawing Figures Patented Sept. 4, 1973 5 Sheets-Sheet 1 FIGJ FIG.(O)

S mm V M F I T= 4.2 liq 6 2.0 (rn m) Effective amplitude of wavinessunder no tension (mm) Patented Sept. 4, 1973 5 Sheets-Sheet 2 UEHEDHHEOUPatented Sept. 4, 1973 3,756,050

5 Sheets-Sheet 3 FIGMZ) f F I G .(O) H O w gu CENTER 3 3i FLAT BUCKLE MQ STRIP 3-5 a"; 2% 5; MB

A B C a F I G (b) F lG.(d)

EDGE w 3 Z, WAVINESS 3 Z) (U 4 (1) H C 'I-IC |I-v-I r-hr! QI E 3 EM (U 3(3 A B C F I G .5

. w I 6 .W- 'H? I I6 m RESJTIFIERS v CONVERTER 1 CIRCUITS Patented Sept.4, 1973 3,756,050

5 Sheets-Sheet strip shape strip shape under no tension under tensioncoiling Ah L o bio (6) machine 7 h; I strip Jl sensor Patented Sept. 4,1973 5 Sheets-Sheet 5 FIG.?

Int! A 4 m Q E mo ww w znmSgow pm co wcwu .Hwuc: mmmcwskz o $25395 953mm u :6

= Effective amplitude of wav1nessurad r' no tension (mm) METHOD ANDAPPARATUS FOR CONTROLLING METAL STRIP SHAPE This is acontinuation-in-part of US. Ser. No. 838,282, filed July 1, 1969 and nowabandoned.

This invention relates to a method and apparatus for controlling theshape of a metal strip during rolling, and more particularly forobtaining a strip having good flatness.

In a process of rolling metal strip, various problems occur incontrolling the gauge and shape of the strip. There is hardly anyproblem in controlling the lengthwise size of strip due to thedevelopment of a known AGC system. However, problems still exist incontrolling the gauge in the direction of the width of the resultingstrip. For example, a report, Theory and Practical Aspects in CrownControl has been published in the Iron and Steel Engineer" August, 1965edition to discuss means of solving such problems. There is however nomeans disclosed for detecting the lateral gauge and shape of the stripin the above report. A prior art solution of the lateral gauge and shapecontrol, utilizing tension rolls and speed detecting rolls which areplaced in the direction of the width of strip, is disclosed in JapanesePatent Publications No. 17429, 1967 and No. 1009, 1968. An experiment toplace thickness meters in the direction of the width was carried out.However, it has been found that all of the above discussed and variousother methods are unstable (that is, provide inconsistent results) andare not serviceable.

An object of this invention is to provide a method of detecting thestrip shape or flatness in the direction of the width of the strip.

Another object of this invention is to provide apparatus for controllingthe strip shape or flatness in the direction of the width of the productstrip.

SUMMARY OF THE INVENTION In accordance with this invention, thevibration or waviness of the strip in the direction of the thickness isdetected at a plurality of locations along the width of the strip whilethe strip is under tension, and then the lateral gauge and shape ofstrip is controlled accordingly during the rolling operation. Thedetecting of the vibration of the strip may be accomplished by detectinga magnetic change, an electrostatic change, or the like, in the strip,without actually contacting the strip, and preliminary control iseffected to control the flatness of the resulting product strip.

The term vibrations as used herein refers to variations of the shape ofthe strip in the direction of its thickness as the strip is moved past afixed location. Thus, with respect to the fixed location, anyundulations or variations in shape of the moving strip will be denotedas vibrations. The greater the undulations of the strip, the greaterwill be the magnitude of the vibrations."

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a and 1b, show examples ofpoorly shaped strips, FIG. 1a illustrating edge waviness and FIG. 1billustrating center buckle;

FIG. 2 is a graph illustrating the correlation between waviness of thestrip in the direction of its thickness when the strip is under tensionand the waviness of the strip when the strip is under no tension;

FIG. 3 is a diagrammatic illustration of an apparatus according to thepresent invention;

FIGS. 4a, 4b, 4c and 4d are graphs illustrating the relationship oftypical strip shapes and the output vibration amplitude corresponding tosaid shapes;

FIG. 5 shows a circuit for detecting vibrations (i.e., waviness) in thedirection of the strip thickness;

FIG. 6 shows a portion of the apparatus to illustrate how the wavinessof the strip under tension is related to waviness of the strip under notension; and

FIG. 7 is a simplified graph similar to that of FIG. 2.

It is generally well known that lack of flatness in the final product,especially in a cold reducing strip mill, is a frequent cause forrejection of the product. The typical causes for rejection arerepresented in FIGS. la and lb. FIG. la illustrateswaves formed at theedges of the strip while FIG. lb illustrates center buckle. Suchundesired shapes should be avoided by controlling the roll crown and/orthe rolling force.

The present invention is the result of experiments which determined thatthe characteristics of wavy edges or center buckle in the resultingstrip under tension during rolling are closely correlated with thevibrating waveform in the direction of the strip thickness. FIG. 2 showsthe correlation between effective amplitude of waviness or undulations(Ah) during rolling and the waviness of the strip (b) under no tension,which was obtained as a result of many experiments.

In the experiments, the value Ah of the low carbon rimmed steel stripswhich are 0.193 mm thick and 768 mm wide is detected between the finalstand of a livestand tandem cold rolling mill and a coiling machine.After rolling of the coil is finished, the coiled strip is removed fromthe coiling machine and uncoiled under no tension, then the value bbeing detected. As the correlations between the vales Ah and b aredifferent, depending upon the tension applied during the rollingoperation, experiments were conducted with respect to three tensions.

According to FIG. 2, it is seen that the amplitude of the vibratingwaveform (i.e., waviness) becomes larger as the magnitude and/or area ofthe strip waviness increases. Such changes in the vibrating waveformduring rolling are detected and then in accordance with the presentinvention, the roll crown and rolling force are automatically adjustedas a function of the differences of the above-detected values. As aresult, good flatness or shape will be easily obtained.

Referring to FIG. 6, the curves of FIG. 2 can be more easily understood.The strip between rolls (R) and coiling machine (C) is under tension.The amount of tension is not constant all through the strip. Even in onestrip, when the tension to which the strip is subjected is varied, therelation between Ah (deviation under tension) and b (deviation under notension) varies as tension in the strip itself varies. The relation isillustrated in FIG. 2 and is as follows:

Ah E b F where i and j are variables indicating the positions of thesensors, m is a parameter relating to tension, and E and F areconstants.

Thus, the relation between Ah and b is defined by a family of curves,each member of which corresponds to a given portion (or position) of thestrip.

In a simplified case, for a given tension in the strip, the curve ofFIG. 7 applies. In FIG. 7 the equation Ah E b F applies, where E and Fare constants. At a given tension, when Ah 0.2, then b 0.93 mm.

When control of the rolling mill is carried out in accordance with thepresent invention, the value Ah is detected by the sensors and fed to acomputing device which then computes the amount of correction requiredto be applied to the roll crown and/or rolling load in order to reduceAh to a small enough value so that the waviness (b) of the output stripunder no tension will be within the desired limits. The value Ah isdetected at various portions of the strip in the direction of its widthand the roll crown and/or rolling load is varied in accordance withdifferences between the detected values of waviness at differentrespective positions along the width to reduce the shape variations inthe resulting output strip. The precise amount of control of the variousparameters in order to produce a flat output strip in accordance withthe present invention will vary, of course, with the particularcharacteristics of the rolling mill and the particular characteristicsof the material being rolled.

FIG. 3 shows an embodiment of the apparatus to carry out theabove-described method in accordance with the present invention.

Referring now to FIG. 3, which shows in part a cold reducing mill, astrip of metal 1 (for example, steel) travels in the direction indicatedby arrows 1 through a predetermined gap between rolls 2. Vibration (orwaviness) detectors 6A, 6B and 6C which are connected with synchronousrectifier circuits 7A, 7B and 7C, respectively, are located at about thecenter portion and on each side of the strip 1, and are suitably spacedfrom strip 1. Changes of thickness or waviness in the direction of thethickness of the stripare detected at various positions along the widthof the strip and are converted to electrical signals by means of thedetectors 6A-6C. The outputs of the synchronous rectifier circuits 7A,7B and 7C are fed to circuits 8A, 8B and 8C, respectively, which convertthe rectifier circuit outputs into center-line values or into signalsrepresenting the effective value of the amplitude of the vibratingwaveform. Differences between the magnitude of the amplitude of thevibrating waveform at the above three points are a function of thethickness or waviness of the strip at the three respective positions. Achange of thickness in the direction of the width can be easilyascertained with the above-described device.

The outputs of circuits 8A-8C are applied to discriminating circuit 9,the output of which is fed to computing circuit 10. Computing circuit 10also receives signals A and B from circuits 8A and 88, respectively.Further provided is a computing circuit 11 which receives signals B andC from circuits 8B and 8C, respectively. Discriminator 9 disablescomputing circuit 10 when A C or when A C.

If a wavy edge occurs at one side of the strip, the amplitude of thevibrating waveform at this positionwill be larger than that of otherlocations. Each vibrating waveform amplitude, in the case of a wavy edgebeing formed on either side of the strip, becomes larger than that ofthe center portion. Conversely, the vibrating waveform amplitude in thecase of center buckle becomes larger at the center than at both sides ofthe strip.

FIGS. 4a-4d show the relationship between vibrating amplitude and stripdefect. The letters A, B and C of FIGS. 4a-4d represent the outputs ofcircuits 8A-8C,

respectively. FIG. 4a shows that the amplitude of the output signals A,B and C are substantially the same and these absolute values are smallin the case of a properly formed strip. FIG. 4b shows the case whereinthe roll crown is too small. Accordingly, a wavy edge is formed at eachside of the strip, as detected by the large vibration amplitude at theedges. In such a case, in accordance with the method of the presentinvention the following steps are automatically implemented:

First, the above outputs A and B of the amplitude circuit are introducedinto a computing circuit 10 (see FIG. 3) wherein the followingcalculation is performed:

A B X An adjusting device 12 (FIG. 3) receives the value X and causesthe pressure of hydraulic cylinders 13 and 13 to increase in accordancewith the value X. This causes the inter-chock pressure 5 and 5' ofbackup rolls 3 to increase. Consequently, the extending rate of thestrip edge portion decreases and the extending rate of the strip at thecenter portion thereof increases.

Such automatic control is continued up to the time when said signal Abecomes equivalent to signal B, as determined by the computing circuit10.

In the case where the signal C is unequal to signal A, such relationshipalso must be dealt with in a similar manner. That is, both signals A andC are introduced into a computing circuit 11 (FIG. 3) wherein thefollowing calculation is done:

A C Y The adjusting device, 14 and 14' for rolling load are caused tooperate in response to the above Y value to adjust the screwdowns l5 and15'. Such control is continued up to the time when signal C isequivalent to signal A, as detected by circuit 11.

Thus, the control of roll crown and rolling load can be automaticallyaccomplished with ease.

FIG. 4c shows values of the vibration amplitude in the case wherein theroll crown is too large and center buckling occurs. Accordingly, thecontrolling steps are effected in reverse of the above-describedcontrolling method.

FIG. 4d shows values of the vibration amplitude in the case wherein bothrolling loads PA and PC are unbalanced. That is, the extending rate inthe direction of the width increases accordingly. The three signals A,B, C have the following relationship:

A B C[notshowninFlG.4]orA B C[as shown in FIG. 4(d)].

In this case, the automatic control system of this invention operates inthe following manner:

First, the functioning of computing circuit 10 is inhibited by thediscriminating circuit 9 which receives signals A, B and C. Secondly,the rolling loads PC and PA are made equal by operation of the computingcircuit 11 which varies PC and/or PA' to make A C Y 0. Thirdly, when theoutput of the discriminating circuit 9 becomes zero, that is, when A C,the function-- ing of the computing circuit 10 is no longer inhibited.Then the crown control is accomplished by means the same steps asmentioned above by adjustment via computing circuit 10 until A B.

It should be clear that the above control functions A, B and C, i.e., bare carried out such that the formula given below also applies:

Ah=E bu+F The. above controls are described with respect to eliminatingedge waviness, center buckle, etc.

FIG. is a view of an embodiment of a vibration sensor which comprises amagnetic core 16 and coil 17 for use as a detector 6A, 6B and 6C in theabove-described system. If such a detector 6 is placed below the strip 1travelling in the direction of arrows l, a change in the gap between thedetector 6 and the strip 1, will be brought about by vibration (or byvariations of the thickness or shape) of the strip in the direction ofthe length of the strip. This vibration (or change of gap) is, ofcourse, converted into a change of coil inductance. An alternatingcurrent bridge 18, wherein one side of the bridge circuit includes thedetecting coil, and which is energized by a power source 19, thendetects an unbalanced voltage corresponding to the above mentionedvibration. This unbalanced voltage is then fed to rectifiers 7 and dealtwith as mentioned above with reference to FIG. 3.

As an alternative to the magnetic circuit of FIG. 5, a circuit utilizingelectro-static capacity, a circuit utilizing photo-electronics, or thelike, can be employed to detect the vibrations in accordance with thepresent invention.

In summary, since the output waviness under no tension is a function ofthe waviness of the strip under tension during rolling, by means of thepresent invention the waviness under tension is measured at a number ofpoints in the direction of the width of the strip and the roll standsare adjusted by a feed forward arrangement in order to equalize thewaviness at the center and edges of the strip, thereby producing productstrips having better flatness.

It should be clear that various modifications and alternations can bemade within the scope of the appended claims.

We claim:

I. A method for controlling the output shape of a metal strip during arolling operation comprising the steps of:

detecting, at the output of a roll stand, the waviness (Ah) of saidstrip in the direction of the strip thickness at a plurality oflocations along the width of said strip; and

selectively controlling the roll crown and the rolling load in responseto the function of b in accordance with the relation Ah E,,,b F, where iand j are variables indicating the position of the sensors, m is aparameter which is a function of tension, b is the output waviness underno tension and E and F are constants, to thereby reduce said shapevariations (b) in the resulting output metal strip to withinpredetermined limits.

2. The method according to claim 1 wherein said detecting step includessimultaneously detecting said waviness at substantially the centerportion of said strip and at each side of said strip.

3. The method according to claim 1 wherein the tension in said stripvaries along the length thereof and the waviness (Ah) during rollingvaries along the length thereof and wherein the term i and j in therelation Ah E b F represent values for given positions along the lengthof said strip.

4. The method according to claim 2 including controlling the roll crownresponsible to the difference between waviness by said center detectorand side detector.

5. The method according to claim 2 including controlling said rollingload responsive to the difference between waviness by said sidedetectors.

6. Apparatus for controlling the shape of a metal strip during a rollingoperation comprising:

a plurality of non-contact detectors located at different respectivepositions along the width of said strip and located at the output of aroll stand of a rolling mill, said detectors detecting the waviness (Ah)of said strip in the direction of the strip thickness during the rollingoperation;

circuit means coupled to said non-contact detectors for generatingsignals representing said detected waviness;

a discriminating circuit coupled to the output of said circuit means;and

control means responsive to the outputs of said circuit means and to theoutput of said discriminating circuit for selectively controlling theroll crown and the rolling load in response to the function of b inaccordance with the relation Ah E b F, where i and j are variablesindicating the positions of the sensors, m is a parameter which is afunction of tension, b is the output waviness under no tension and E andF are constants, to thereby reduce the waviness in the resulting outputmetal strip to within predetermined limits.

7. Apparatus according to claim 6 wherein said detectors are spaced fromsaid strip.

8. Apparatus according to claim 6 wherein said detectors are located atsubstantially the center of said strip and at each side of said strip.

9. Apparatus according to claim 8 wherein said control means controlsthe roll crown responsive to the difference between the wavinessdetected by said center detector and side detector.

10. Apparatus according to claim 8 wherein said control means controlssaid rolling load responsive to the difference between the wavinessdetected by said side detectors.

11. Apparatus according to claim 8 wherein said discriminating circuitis responsive to predetermined variations in said waviness to inhibitcontrolling of said rolling load.

12. Apparatus according to claim 11 wherein said discriminating circuitis responsive to signals indicating that said waviness caused bymaladjustment of roll crown have been substantially eliminated to causesaid control means to control said rolling load to substantiallyeliminate waviness in said output strip.

13. Apparatus according to claim 6 wherein said control means includesfirst computing means responsive to predetermined waviness variationsfor controlling said roll crown and second computing means responsive tothe other predetermined waviness variations for controlling said rollingload.

a a a :0- s

1. A method for controlling the output shape of a metal strip during arolling operation comprising the steps of: detecting, at the output of aroll stand, the waviness ( Delta h) of said strip in the direction ofthe strip thickness at a plurality of locations along the width of saidstrip; and selectively controlling the roll crown and the rolling loadin response to the function of bij in accordance with the relation Deltah Embij + F, where i and j are variables indicating the position of thesensors, m is a parameter which is a function of tension, b is theoutput waviness under no tension and E and F are constants, to therebyreduce said shape variations (b) in the resulting output metal strip towithin predetermined limits.
 2. The method according to claim 1 whereinsaid detecting step includes simultaneously detecting said waviness atsubstantially the center portion of said strip and at each side of saidstrip.
 3. The method according to claim 1 wherein the tension in saidstrip varies along the length thereof and the waviness ( Delta h) duringrolling varies along the length thereof and wherein the term i and j inthe relation Delta h Embij + F represent values for given positionsalong the length of said strip.
 4. The method according to claim 2including controlling the roll crown responsible to the differencebetween waviness by said center detector and side detector.
 5. Themethod according to claim 2 including controlling said rolling loadresponsive to the difference between waviness by said side detectors. 6.Apparatus for controlling the shape of a metal strip during a rollingoperation comprising: a plurality of non-contact detectors located atdifferent respective positions along the width of said strip and locatedat the output of a roll stand of a rolling mill, said detectorsdetecting the waviness ( Delta h) of said strip in the direction of thestrip thickness during the rolling operation; circuit means coupled tosaid non-contact detectors for generating signals representing saiddetected waviness; a discriminating circuit coupled to the output ofsaid circuit means; and control means responsive to the outputs of saidcircuit means and to the output of said discriminating circuit forselectively controlling the roll crown and the rolling load in responseto the function of bij in accordance with the relation Delta h Embij +F, where i and j are variables indicating the positions of the sensors,m is a parameter which is a function of tension, b is the outputwaviness under no tension and E and F are constants, to thereby reducethe waviness in the resulting output metal strip to within predeterminedlimits.
 7. Apparatus according to claim 6 wherein said detectors arespaced from said strip.
 8. Apparatus according to claim 6 wherein saiddetectors are located at substantially the center of said strip and ateach side of said strip.
 9. Apparatus according to claim 8 wherein saidcontrol means controls the roll crown responsive to the differencebetween the waviness detected by said center detector and side detector.10. Apparatus according to claim 8 wherein said control means controlssaid rolling load responsive to the difference between the wavinessdetected by said side detectors.
 11. Apparatus according to claim 8wherein said discriminating circuit is responsive to predeterminedvariations in said waviness to inhibit controlling of said rolling load.12. Apparatus according to claim 11 wherein said discriminating circuitis responsive to signals indicating that said waviness caused bymaladjustment of roll crown have been substantially eliminated to causesaid control means to control said rolling load to substantiallyeliminate waviness in said output strip.
 13. Apparatus according toclaim 6 wherein said control means includes first computing meansresponsive to predetermined waviness variations for controlling saidroll crown and second computing means responsive to the otherpredetermined waviness variations for controlling said rolling load.